1. Field of the Invention
The present invention relates to an ultrasonic motor that is driven by elliptic vibration formed by combining longitudinal and twisting vibrations, and more particularly to an improved motor structure for converting the longitudinal vibration to the twisting vibration, or vice versa.
2. Description of Related Art
A standing-wave-type ultrasonic motor driven by elliptic vibration that is a compound of longitudinal and twisting vibrations is known. An example of this kind of motor is shown in FIG. 29. The ultrasonic motor is composed of a stator 500 and a rotor 504. The stator 500 includes a pair of metallic blocks 502 and 503, between which a pair of piezoelectric elements 501 is interposed, constituting a Langevin-type vibrator. The metallic blocks 502, 503 and the piezoelectric elements 501 are fastened together, thereby forming the stator 500. The rotor 504 is mounted on the stator 500 by a through-bolt so that the rotor 504 silidably rotates on the upper surface of the stator 500. Longitudinal vibration is generated by the piezoelectric elements, and a part thereof is converted into twisting vibration by slits 505 formed on the metallic block 503. The longitudinal and the converted twisting vibrations are combined into elliptic vibration which appears on the upper surface of the metallic block 502. The rotor 504 is driven by the elliptic vibration. The slits 505 are formed on the outer periphery of the metallic block 503 by machining with a certain depth. Conventionally, the slits 505 are machined with an end mill, a metal saw or the like. However, such machining is not easy, and it is expensive to machine all the slits on the outer periphery of the metallic block.